runtime-sdk: not-module-specific error type desired

imported from a discussion on slack:

• more and more formerly centralized services done in the dispatcher are now becoming module-controlled
• we used to have these processes use modules::core::Error as their error type
• when we expanded stuff out to modules, we kept that error type as is
• modules do whatever, and we ended up adding a bunch of wrappers in modules::core::Error to handle whatever other complaints come from modules
• to break out of this practice of making more and more wrappers in modules::core::Error, we'd need a more general error type
• RuntimeError (the module-code-message tuple from the oasis-core side) is general enough, but lacks the abort-ness information
• module::CallResult can retain abort-ness information, but it's coupled into a Result-like enum, and it's hardcoded to have a cbor::Value payload on the Ok branch
• I guess Box would be fine, but eh, extra allocations

Start by comparing the requirements for modules::core::Error, RuntimeError, and module::CallResult described in the issue. Determine how a general error type can retain abort information without a fixed cbor::Value payload or additional wrappers. Done means the runtime SDK has an agreed implementation direction that addresses these trade-offs.